The present invention relates generally to oil management and oil level equalization in the sumps of parallel, manifolded compressors in a refrigeration system. More specifically, the present invention relates to the maintenance of equal oil levels in the sumps of hermetic compressors in a parallel compressor refrigeration system through the employment of apparatus which insures that equal amounts of suction gas and entrained oil are delivered to the shells of operating compressors by maintaining the pressures in the shells of operating compressors equal.
It is well documented that when low-side compressors are employed in a parallel arrangement in a refrigeration system, the tendency exists for one of the compressors to become starved for lubricating oil. Low-side compressors are those in which suction gas is essentially dumped into the interior of the shell of the compressor from where it is drawn into the motor-compressor housed within the shell.
The hermetic shells of low-side refrigeration compressors house motor-compressor units and generally define lubricating oil sumps at their bottoms. A portion of the motor-compressor lubricating oil, which collects and is stored in such sump areas, becomes entrained in the suction gas drawn into the motor-compressor and travels with the suction gas into, through and out of the motor-compressor. The lubricating oil is carried through the refrigeration system entrained in the system refrigerant and eventually makes its way back to the suction line by which the refrigerant is returned to the parallel compressor arrangement in the system.
When suction gas is returned from the evaporator to the compressors in a parallel compressor refrigeration system it is inevitable that one of the compressors will draw more suction gas, and consequently more entrained lubricating oil, into its shell than will the other compressor or compressors. Over a period of time, and unless otherwise accounted for, at least one of the compressors will become starved for oil and ultimately will fail.
Many oil level equalization schemes for parallel compressor refrigeration systems are known. Such systems may include an oil line leading from a common oil reservoir to the individual sumps of the multiple system compressors as is illustrated in U.S. Pat. Nos. 3,581,519 to Garrett; 3,777,509 to Muench and 4,530,215 to Kramer. Typically, such systems require the use of pumps, eductors or the like to move oil from a common oil storage area to the individual sumps of the individual system compressors. In such systems, the sump pressures of the individual compressors are typically unequal and the oil level in individual compressors is mechanically maintained or assisted.
In other systems, more passive means of equalizing oil levels in the sumps of parallel compressors are employed which do not rely on the accumulation of oil in a common reservoir. Exemplary in this regard are U.S. Pat. Nos. 4,411,141 to Hara and 4,551,989 to Lindahl et al. which employ a lubricant non-return valve and suction piping of predetermined unequal sizes respectively to accomplish more passive and mechanically simple oil management in a manifolded parallel compressor arrangement.
The need continues to exist for a reliable, mechanically uncomplicated and self-regulating arrangement by which the oil levels in parallel compressors in a refrigeration system are maintained at least at a predetermined minimum level.